1) Field of the Invention
The present invention relates to a technology for more effectively recording and playing-back information in and from a recording medium.
2) Description of the Related Art
In conventional magnetic disk apparatus, servo information may be erased when a speed of a recording medium deviates from its standard speed, or when a data write starting position shifts due to rotational variation and decentering of the recording medium. To avoid erasing of the servo information due to such factors, gaps are provided in a recording medium.
FIG. 9A illustrates a conventional recording format in a magnetic disk apparatus. As shown in FIG. 9A, a servo frame delimited by SSMs includes a Servo (servo information) 30, sectors (SECs) 40, and GAPs (GAPs) 20, and is structured such that the servo information is not overwritten even when a data write starting position shifts.
In other words, sector pulses are generated at predetermined timing after an SSM is detected, and the data is written with reference to the sector pulses. Even if the generation timing of the sector pulse shifts, the GAP 20 ensures that the Servo 30 is not overwritten.
However, when many GAPs 20 are provided in the recording medium, sector lengths shorten, whereby format efficiency reduces, or there is a need to increase recording density. Japanese Patent Application Laid-Open Publication No. 1999-31358 discloses a disk synchronous write system in which the GAPs 20 are eliminated, a distance between servos is measured using the servo synchronous marks, a variation in the number of revolutions of the recording medium is determined, and timing signals for an optimum read gate and write gate are generated accordingly, thereby enhancing the format efficiency.
FIG. 9B illustrates a recording format in a magnetic disk apparatus that uses the disk synchronous write system. As shown in FIG. 9B, when the disk synchronous write system is utilized, write is executed in synchronization with the recording medium, and therefore, variations in write position are eliminated, thereby making it possible to remove the GAPs 20 shown in FIG. 9A. As the result, the SEC 40 can be made longer, thereby enhancing the recording density.
However, when the SSMs on a track are equidistant, after one rotation of the track, extra or insufficient space is generated at the last servo frame, which is a servo write linking position. FIG. 9B illustrates a case in which an insufficient space is generated in the servo write linking position, resulting in a shorter distance between the SSMs. As in this case, when the distance between SSMs becomes shorter in a servo write linking position, there is a possibility that the next Servo 30 is erased.
Thus, even when the disk synchronous write system is used, a GAP 20 is provided in consideration that a distance between SSMs may become shorter in a servo write linking position. FIG. 9C illustrates a recording format in a magnetic disk apparatus in which the disk synchronous write system is used, and GAPs 20 are provided to protect write linking. As shown in FIG. 9C, although the GAP is smaller compared with that of the conventional recording format shown in FIG. 9A, the GAPs 20 are provided.
However, GAPs 20 that are provided in ordinary positions other than the servo write linking position to protect the servo write linking position, prove unnecessary. Moreover, the sector length becomes shorter, which gives rise to a problem that there is a need to increase the recording density to maintain recording capacity.